1. Field of the Invention
The present invention relates to a charged particle beam application apparatus suitably used to machine semiconductors, and in particular, to a sample movement mechanism in a charged particle beam application apparatus.
2. Background Art
With an increase in the degree of integration of semiconductor devices and a decrease in their size, it has become essential in the market to improve the yield of semiconductor devices by eliminating defective processes. A process of manufacturing semiconductor devices using wafers generally analyzes defects using an inspection-scanning electron microscope (SEM) that compares and checks circuit pattern images using a SEM, a critical dimension scanning electron microscope (CD-SEM) that measures the width or the like of circuit patterns using a SEM, or a transmission electron microscope (TEM) having a higher resolution.
Further, to use a transmission electron microscope to observe and analyze defects in a circuit pattern, an ion beam machining apparatus using a focused ion beam (FIB) is used as means for producing a sample. For example, JP Patent Publication (Kokai) No. 05-52721 discloses a method of separating a sample from a wafer.
The series of inspection steps require the early discovery of defects and the quick feedback of this information to the process. Accordingly, an apparatus using a plurality of charged particle beams is desired which eliminates a time loss resulting from differences in the time of delivery and reception of wafers or samples between apparatuses or differences in operability between the apparatuses to put the apparatuses together or make them inline.
For example, JP Patent Publication (Kokai) No. 11-213935 discloses a dual beam apparatus using charged particles from an ion particle beam machining apparatus and a scanning electron microscope. As shown in FIG. 6, this apparatus has an ion particle beam machining apparatus column 601 and a scanning electron microscope column 602 arranged at a certain angle. A machined or observed point of a sample 607 on a stage 618 is irradiated with charged particle beams drawn out of an ion source 603 and an electron gun 609. The stage 618 is a U-centric staged with four axes for horizontal two-dimensional movements, rotations, and inclinations. A stage control section 619 is controlled by a host controller 614.
In this case, the U-centric function is effective only if the observed point of the ion charged beam machining apparatus coincides with the observed point of the scanning electron microscope. Even if the ion charged particle beam machining apparatus and the scanning electron microscope are centered, the observed points may deviate from each other when the optical conditions for the ion charged particle beam machining apparatus and scanning electron microscope are changed.
Further, it is assumed that the U-centric function does not have a stage (Z stage) for the direction of height of the sample. If for example, the sample is a semiconductor wafer of φ300 mm, it may be bent by 200 μm in the direction of the sample height. Accordingly, it may be disadvantageous in a practical sense to electrically control the optical system to focus the sample surface because an optical resolution (magnification) is in inverse proportion to the range of the control.
Various well-known examples have been disclosed in connection with the focal distance of the ion particle beam machining apparatus and scanning electron microscope as well as a method of controlling an optical condition, that is, the focal distance. For example, JP Patent Publication (Kokai) No. 7-176285 discloses an automatic focusing mechanism of the scanning electron microscope.
As shown in FIGS. 7 and 8, in the automatic focusing mechanism of the scanning electron microscope disclosed in JP Patent Publication No. 7-176285, an objective 703 focuses an electron beam 701 generated by an electron gun (not shown) and irradiates a sample 704 with the electron beam 701. A stage 715 on which a sample is placed receives coordinate data on a point to be measured from a wafer information file 716 in which the coordinates of the measured point are registered. The stage 715 moves the wafer to the appropriate measured point. X deflection coils 702X and 702Y are used to scan the electron beam 701 over the sample. A detector 714 detects secondary electrons 714 generated by the sample 704 and transmits them to a focused point detecting device 710 via an amplifier 706. The focused point detecting device 710 is composed of a focus control device that sequentially varies an excitation current for the objective 703 step by step, a signal intensity differential device that differentiates the intensity signal, and a peak detecting device that determines a peak of a differential value of the intensity signal. These arrangements enable the focal distance, that is, the focal height of an electron beam shown in FIG. 8 to be automatically adjusted by determining the differential value of the secondary electron signal to control the objective.
If the charged particle beam is not applied perpendicularly to the sample surface as in the case of the previously described well-known example (JP Patent Publication (Kokai) No. 11-213935), a change in focal distance changes the focus position in a horizontal direction of the sample surface. Accordingly, the system must be complicated in order to correct optical conditions for the deflection coils in addition to the objective.
JP Patent Publication (Kokai) No. 200-251823 discloses a method of inclining a sample (sample stage) to change the focal distance n the basis of the sample and a charged particle beam and using an image shift function to correct the amount of bending. This publication describes a method of correcting bending in the X and Z directions or in the Y and Z directions which may occur when an axis of tilt is changed particularly if there is a deviation between the observed position of the sample and an U-centric axis as shown in FIGS. 9 and 10. The correction is carried out on the basis of optical conditions, that is, by using an electric image shift function or using a motor to mechanically drive the stage.
However, this method must use a certain method of measurement to prestore, for each inclination, the relationship between the X and Z coordinates, which is a basis for conversions of the amount of bending. However, this relationship is a mechanical specific parameter, so that if the relationship between the sample and the axis of tilt of the stage is changed as a result of replacement of the sample or the like, the parameter must be measured again.
[Patent 1]
JP Patent Publication (Kokai) No. 05-52721
[Patent 2]
JP Patent Publication (Kokai) No. 11-213935
[Patent 3]
JP Patent Publication (Kokai) No. 7-176285
[Patent 4]
JP Patent Publication (Kokai) No. 2000-251823